1. Field of the Invention
The present invention relates to a system and method for managing node communications in a wireless ad-hoc network based upon node activity status. More particularly, the present invention relates to a system and method for detecting communication requirements in a network and placing nodes in an inactive state where conditions allow. Detection of increased communication requirements is used to place nodes in various stages of activity and to alter network communication routes based upon node activity levels in the network.
2. Description of the Related Art
In recent years, a type of mobile communications network known as an “ad-hoc” network has been developed to address the needs of multiple mobile device communication beyond traditional infrastructure coverage. In this type of network, each user terminal (hereinafter “mobile node”) is capable of operating as a base station or router for other mobile nodes within the network, thus eliminating the need for a fixed infrastructure of base stations. Accordingly, data packets being sent from a source mobile node to a destination mobile node are typically routed through a number of intermediate mobile nodes before reaching the destination node.
More sophisticated ad-hoc networks are also being developed which, in addition to enabling mobile nodes to communicate with each other as in conventional ad-hoc networks, further enable the mobile nodes to access fixed networks and communicate with other types of user terminals, such as those on the public switched telephone network (PSTN) and the Internet. Details of these advanced types of ad-hoc networks are described in U.S. patent application Ser. No. 09/897,790 entitled “Ad Hoc Peer-to-Peer Mobile Radio Access System Interfaced to the PSTN and Cellular Networks”, filed on Jun. 29, 2001, in U.S. patent application Ser. No. 09/815,157 entitled “Time Division Protocol for an Ad-Hoc, Peer-to-Peer Radio Network Having Coordinating Channel Access to Shared Parallel Data Channels with Separate Reservation Channel”, filed on Mar. 22, 2001, and in U.S. patent application Ser. No. 09/815,164 entitled “Prioritized-Routing for an Ad-Hoc, Peer-to-Peer, Mobile Radio Access System”, filed on Mar. 22, 2001, the entire content of each being incorporated herein by reference.
In such ad-hoc networks, data flow is from node to node, and relies heavily on optimum route selection. Factors such as transmission power consumption and pipeline delays play a critical role in selecting transmission routes through the network. For example, certain service classes such as voice data, requires minimal pipeline delays during transmission. However, minimizing pipeline delays often increases transmission power levels, which may overly burden the limited power supply of mobile nodes. One approach to improving mobile node power consumption efficiency includes placing nodes into varying degrees of inactivity, as allowed by communication requirements.
For example, when a node in a network is not active, it can go into a more dormant state where it can send fewer packets, thus reducing its over-the-air bandwidth consumption, and significantly reduce the power drain on its battery and the batteries of other nodes which receive those packets, to achieve maximum useful life for the node batteries. This is especially useful when considering the deployment of remote sensor nodes where long life of node batteries is critical. Sensor nodes are nodes which are capable of performing the node functions described above, but can also monitor, for example, environmental conditions such as temperature, humidity, wind, and so on. Such sensor nodes, or sensors, belong to a class of devices that need to have network capability, but utilize the network sporadically, and are potentially inactive for long periods of time.
As can be appreciated by one skilled in the art, nodes in a network not only transmit, receive and route packets of information from node to node within the network, but also transmit, receive and route packets to and from nodes located beyond the network. Nodes in the ad-hoc network generate these packets, which may be classified as either data packets or control packets. The distinction between data and control packets allows node participation within the network to be modified based on whether or not the node is active at a given point in time. That is, data packets include packets which are generated by the user and perform some activity, such as using streaming video applications. Control packets are created to discover other nodes, build routing tables and share network topology between nodes. Therefore, as among network nodes, sending and receiving control packets with greater frequency results in more accurate and complete knowledge of the network.
A problem with frequent packet transmission, however, is that node transmitters used in packet transmission typically are the largest power consuming component of the node. Therefore, for each instance where node transmitter use may be avoided by not sending messages, significant power consumption savings can be achieved. However data packets, as compared to control packets, may not be avoided to the same extent, as data packets are generated by the user and perform some activity. Control packet transmissions however, may be reduced in situations where the need for node updates are smaller.
Ad-hoc networks typically require a mechanism by which to discover other nodes, build routing tables and share network topology amongst the nodes. This is achieved using messaging that is typically described as overhead messaging, and may contain control packet transmissions. Control packet transmissions are required, for example, to the extent node updates are needed. Therefore, reducing the need for frequent node updates is one approach to reducing transmitter usage in network nodes. Many ad-hoc networks typically have update rates that are in the order of 1 to 5 seconds, based on the presumption of high rates of change and high traffic demand. One approach to reducing node updates has been to design a network where the network nodes are synchronized and all “wake up” at the same time to share information. However, this is not always an effective technique of achieving power savings through reduced node activity. For example, in such an arrangement, because a node cannot transfer data until the “wake up” time, frequent update delays may result. Furthermore, the network nodes cannot always be easily synchronized with one another. Implementing data updates at “wake up” is particularly difficult in a mobile ad-hoc network where nodes join and leave the network arbitrarily and on a regular basis.
Accordingly, a need exists for a system and method to reduce the frequency of control packet transmissions in an ad-hoc network, thereby reducing demand on limited power supplies at mobile nodes.